A 3D printing process may use a feedstock material, extruded from a print head, to additively manufacture a part by layering the feedstock material. The feedstock material may comprise a polymer and reinforcing fibers, such as carbon fibers, which are opaque to visible and ultra-violet light. When the polymer in the feedstock material is a photopolymer, a source of curing energy may be directed at the feedstock material, dispensed by the print head, to solidify the feedstock material. However, when the reinforcing fibers are opaque to the curing energy, they cast shadows and prevent the curing energy, originating directly from the source of curing energy, from irradiating and curing the photopolymer in the shadows.